Waterproofing leather



JUL: 2%, 19% c. s. SHAW WATERPROOFING LEATHER Filed May 13, 1946 WNMWWNWW ENVENTOR Patented June 20, 1950 UNITED STATES PATENT OFFICE 4 Claims.E

This invention relates to improvements in the art of waterproofingleather by impregnating it with fats and greases.

The term waterproofing as used herein refers to the art of incorporatingwaterproofing substances in leather but is not intended to imply thatthe leather is rendered absolutely impervious to water. The term"impregnating as used herein means the substantially complete filling ofthe voids or the air spaces in the leather by the waterproofingcompound.

The principal object of the invention is the provision of waterproofedleather which, while impregnated with fats or greases, has the normalappearance, feel and springiness of non-waterproofed leather; is capableof being channelled, buifed, finished and cemented in accordance withconventional shoe-factory methods; and has a non-greasy surface which,in contact with '-.wet pavements, has a relatively high coeillcient offriction which compares favourably with that of non-waterproofed leatherand substantially reduces the hazard of slipping as compared with soleleather in which fatty and greasy waterproofing substances have beenincorporated in accordance with prior art procedures.

The foregoing object is achieved by impregnating leather, particularlysole leather, with waterproofing substances selected from the classcomprising hard high melting point fats and waxes; then, withoutdamaging the leather, effecting substantial removal of the fats orgreases from the grain and fiesh sides to a depth sufllcient to enablethe leather to be buffed, channelled, finished, or cemented inaccordance with conventional shoe-factory methods; and then cooling theleather so that the waterproofing substance left in the interior portionof the leather is solidified to a hard brittle condition in which it isfixed against migration or absorption into the outer portions and isresistant to the displacing or squeezing-out effect of the high internalpressure created in the leather when the latter is wet and the fibresthereof are swollen by absorption of warm water.

The fats and greases employed in accordance with my invention are thosewhich have a relatively sharp softening range and with melting point notsubstantially below 120 F. and which, at normal temperature, are hardand brittle. Because of their high melting temperatures such fats andgreases will not migrate or exude into the fat and grease free outerportions of the leather when subjected to the heat of the foot or to theheat of summer temperatures or of warm, sand such as might be met within the 'wear conditions. A fat approaching full hydrogenation such ashydrogenated tallow may be mentioned as a specific example of a hard,high melting point waterproofing substance which maybe used inaccordance with my invention. This substance has been found satisfactoryfor waterproofing sole leather for service in Europe and America. Inwaterproofing sole leather for service in extremely hot climates it hasbeen found beneficial to raise the melting point by addition of asuitable substance such as fully hydrogenated castor oil. In general,however, carnauba wax or any waterproofing fat or grease substance-orcompound having a sharp melting point not substantially below 120 F. maybe advantageously employed in accordance with my invention.

In the practice of my invention the leather is dried, immediately priorto impregnation, at a temperature of, preferably, 100 F. to 140 F.,until the moisture content is brought to a very low percentagethroughout the leather. The dried leather is then impregnated, with ahard fat, until the leather has absorbed the desired amount of fat, theimpregnation being usually continued until all the air spaces and voidsin the leather are substantially completely filled by the fat. Theimpregnation is preferably accomplished by dipping the leather in a tankcontaining the melted fat and permitting the leather to remain thereuntil the absence of air bubbles indicates complete filling of theleather by the fat. Alternately, the fat may be incorporated invegetable tanned leather by a stufling procedure in a hot air drumsimilar to that employed in stufllng harness leather. Other suitablemethods of impregnation may also be employed.

Following impregnation thereof, the leather is brieily drained off orhung in an atmosphere well above the melting temperature of theincorporated waterproofing substance until the surface is quite drainedoff and dry looking. Appreciable cooling of the leather during thisstage of the process is undesirable.

The leather is then washed with an aqueous solution of a, suitabledetergent until the surface film of fat has been removed and theappearance of .the leather indicates that it is uniformly wet by theaqueous solution. The temperature and/or time factors of this washingtreatment, which is necessarily carried out at a temperature above therelatively high melting temperature of the waterproofing substance, mustbe controlled or regulated to prevent damage to the leather. Agitationor scrubbing may be employed during this washing treatment but theremoval of the dim of fat is due mainly to the fact that ailinity of thedetergent solution for wetting the fibres of the leather is greater thanthat of the waterproofing substance. As an example of detergents whichmay be employed in this washing procedure I may mention sulphated fattyalcohols which are suitable in solutions maintained at an effectiveacidity of approximately pH 3. The concentration of the detergentsolution is a variable factor, being adjusted to suit variousconditions. In many cases, using a solution of sulphated fatty alcohol,a solution of 1% to 2% has been found efllcient.

In connection with the washing of the leather with the detergentsolution at a temperature above the relatively high melting temperatureof the waterproofing substances, it is important to note that ordinaryvegetable tannages differ considerably in their ability to resist heatin the presence of water or aqueous solution and that therefore timefactor of the washing operation is important.

when dealing with the washing of vegetable tanned leather with asolution of sulphated fatty alcohol the washing may be carried out intwo stages in which temperature and time factors are controlled to avoiddamage to the leather. The initial washing of the fat film from theleather is preferably done at a temperature of about 150 F. which, insome cases, may be too high for the period of time required to wet theleather with the aqueous solution to the depth of the grain layer orsuch other depth as it may be desired to clean the waterproofingsubstance from the interior of the grain and/or flesh layers. In thosecases where prolonged washing at 150 F. is apt to damage the leather,the leather is initially washed at this temperature for a relativelyshort period, say two or three minutes, and is then given a secondwashing or soaking with the detergent solutionat a temperature ofapproximately 130 F. for a period of from about 20 minutes to threequarters of an hour or longer, depending on the depth to which thewaterproofing substance is to be removed from the grain and/or flesh ofthe leather. The concentration of the detergent solution used in thesecond stage washing may be reduced as com-,

pared with that used in the first stage, since the capillarity of thefibres as modified by the first stage washing enables the detergentsolution used in the second stage to readily penetrate the leather andswell the fibres by absorption of aqueous solution so that a largeportion of the waterproofing substance, which is softened and exuded atthe temperature used in the second washing, is squeezed out.

when the washing of the impregnated leather with the detergent solutionis carried out in an immersion tank, the surface of the solution, atleast where the leather is removed from the tank,

should be skimmed free of the softened or melted fat which rises andfioats on the surface in considerable quantity.

The second washing or soaking of the leather with the detergent solutionremoves large amounts of the waterproofing substances from the grain andleaves it in a condition in which it may be lightly buffed with a newsharp bufilng paper. However, in order to condition the leather forsatisfactory buiilng and channelling it is necessary to resort to afurther carefully controlled slicking or scudding operation to squeezeor slick out the greater portion of the remaining fat or greasywaterproofing substance from the grain and flesh sides of the leather.This final treatment of the leather may be accomplished by subjecting itto a scudding or s1ick-. ing operation on a suitable scudding machinesuch as the Whitney Model P scudding machine which is equipped withsetting-out" cylinders which have been found very advantageous for thepurpose. The Whitney machine includes a spraying device which sprays thesurface of the leather with detergent solution while contacted by thecylinders. For the purpose of the present invention the Whitney machinemay be equipped with additional spraying devices, one of which isarranged to spray the flesh side of the leather prior to the entry ofthe leather into the feed rolls to thereby enable a considerable amountof waterproofing substance to be squeezed out of the flesh side by thefeed rolls. The solution fed to the sprays preferably contains somedetergent and is heated to a temperature of F. to F. This solution ispreferably fed to the sprays by a recirculating pumping system.

Following the final cleaning of the waterproofing substance from theinterior of the grain and flesh layers by the slicking or scuddingtreatment, the leather is hung up in a cool place or dipped in coldwater so that the waterproofing substance left in the interior portionof the leather will quickly chill and have little or no tendencythereafter to migrate into or be absorbed by the leather in the grain orthe flesh. In this connection it will be understood that if thetemperature of the leather were maintained at, say, 120 F. after theslicking or scudding operation, then the waterproofing substance whichis softened or melted at this temperature would be absorbed among thefibres in the grain as the water evaporates and would thus spoil thewhole effect.

Similarly, if portions of the impregnating compound cr substance remainliquid long after other portions have crystallized or hardened, as mightbe the case in a mixture of fats covering a wide melting range, the fator fats having the lower melting temperature may either migrate into thegrain of the leather as the water evaporates therefrom or besubsequently squeezed or forced by capillary action from the interior ofthe leather into the grain by absorption into the leather fibres of theinterior portion of some of the water from the grain layer.

In the case of a hard fat and a cool temperature, the continuedabsorption of water into the interior portion of the leather from thegrain layer will not force the fat from the interior into the grainlayer of the leather as would be the case if any portion of the fat weresoft at normal temperatures. This is an important point to bear in mindin connection with the present invention since, in order that the fatmay stay where it is desired, 1. e. in the interior portion of thevsdeather, it must have sufficient hardness to resist the pressurewithin the structure of the impregnated leather due to the capillarityor absorption of water by the leather fibre itself. As an example, aproperly impregnated vegetable tanned sole leather as produced by myinvention would, when immersed in water during a tempering operation ina shoe factory, be wet to the full depth of the grain layer in arelatively short time and the grain would be soft and easily channelledas in ordinary leather. Prolonged soaking, however, will produceabsorption of water by the fibres in the interior at a very greatlyreduced rate and, at the same time due to the swelling of the leatherfibres in the interior portionof the leather, create a heavy internalpressure on the waterproofing compounds which lie between fibrils andfibre bundles of the hide structure in the interior portion of theleather as the waterproofing compound is not soluble in the leatherfibre substance itself as is water. This pressure may be readilyrecognized by the fact that a sole treated by my method being immersedfor, say, 24 hours will be peculiarly firm and perhaps even firmer thanbefore wetting and will sometimes be curled by the pressures created inthe outer strata of the interior portion of the leather. In someinstances this pressure created is so great when the leather isimpregnated with really hard fats that the water appears to no longerenter the leather. From this it will be apparent that, compared with thesofter lower melting temperature fats and those of a plastic nature atnormal temperatures which have previously been employed for impregnatingleather in accordance with prior art practice, the hard high meltingpoint fats or compounds employed in accordance with my invention may bemore advantageously used both to ensure a higher degree ofwaterproofness and to maintain the position of the waterproofingsubstance where it is most desired and in a condition such that it willnot migrate or be squeezed out during tempering of the leather and thusinterfere with the subsequent shoe making operations such as bufiing andchannelling operations.

The condition in which the leather is left following the slicking orscudding treatment is illustrated by the accompanying drawing, in whichthe single figure is a cross sectional view of a piece of sole leather.In this figure the showing to the left of the vertical line AAillustrates the condition of leather which has been subjected towaterproofing and subsequent cleaning operations in accordance with myinvention, while the showing to the right of said line illustrates thecomparative condition of leather which has been waterproofed withrelatively low temperature waterproofing substances and then surfacecleaned in accordance with prior art procedures.

Referring more particularly to the drawing,

the dotted line BB represents the approximate line of demarcationbetween the grain layer C and the interior portion D of the leather; thedotted line E-E' represents the approximate line of demarcation betweenthe interior portion D and the flesh layer F; and the dotted line G-Gindicates the depth to which the hair holes H and the grain C areordinarily cleaned of waterproofing substances when the leather isimpregnated and cleaned in accordance with prior art practice.

With reference to the condition of the leather appearing to the right ofline AA it will be noted that the grain layer C and the hair holes H arefilled up to the line G-G with finely dispersed particles J ofwaterproofing compound which interfere with satisfactory bufilng oftheleather to the required depth and also with the wetting of the grainlayer C to the depth necessary to permit of easy and satisfactorychannelling of the leather. It will also be noted that the flesh layerof the leather appearing to the right of the line AA contains asubstantial amount of relatively large particles K of waterproofingcompound which interfere with the cementing of the leather and give riseto other disadvantages.

In connection with the foregoing description of the condition of theimpregnated and cleaned leather appearing to the right of line AA, itmay be explained what prior proposals for impregnating leather with fatsand greases have been based on the use of parafiine wax and relativelylow melting point materials such as Vaseline and other waterproofingfats and greases which are comparatively soft at normal temperatures. Incleaning the grain and/or flesh layers of leather impregnated with thesewaterproofing substances, the cleaning temperatures employed, whileabove the melting temperatures of the waterproofing substance, have beentoo low to give more than a superficial cleaning of the grain layer C tothe shallow depth represented. by the line GG. The use of hard fats andgreases apparently was avoided because of the fact that their meltingtemperatures lie above or close to the temperatures at which damage toleather, particularly vegetable tanned leather, would ordinarily beexpected. The damage would result from using prior art method ofprolonged cleaning of the grain and flesh layers of the impregnatedleather with an aqueous solution at a temperature above the relativelyhigh melting temperature of the hard fats and greases such as areemployed in accordance with my invention.

The relatively soft waterproofing substances employed in accordance withthe prior art practices referred to do not have either a high meltingpoint or a short plastic range. On the contrary, they have either orboth a low melting point or a long plastic range. When leatherimpregnated with these low-melting point or long plastic range materialsis bent it has a leady" feel and loses its springiness and does notreadily lend itself to the production of comfortable well made footwear.

When the internal pressure of leather impregnated with soft, low meltingpoint waterproofing substance is increased by swelling of the leatherfibres due to absorption of water, an appreciable amount of therelatively soft waterproofing substance is squeezed out of the leatherso that, as the leather is repeatedly wet and dried, its resistance towater absorption is greatly lowered. Such impregnated leather maytherefore have three times the water absorption of one incorporating ahigher melting point hydrogenated tallow or similar hard, high meltingpoint waterproofing substance which, at normal temperature, issufiiciently hard and brittle to stay placed in the interior portion ofthe leatherv despite repeated wetting and drying of the leather underservice conditions or during tempering, channeling, or processing of theleather subsequent to its impregnation with the waterproofing substance.

Reverting again to the drawing, it will be noted that the grain C andhair holes H of the leather appearing at the left of line AA are free ofwaterproofing compound to the full depth of the grain and that the fieshside or layer F is also free of the waterproofing substance. This is thepreferred condition in which the leather is left by the impr nating,detergent-cleaning, and clicking or scudding operations comprising myinvention. Such leather can be worked in a similar manner asnon-waterproofed leather and ha essentially.the same appearance, feeland springiness. During the bumng operations the depth to which thegrain layer has been cleaned of the waterproofing substance and thenature of the waterproofing substance itself prevents any possibility ofmelting and migration of said waterproofing substance into the grainlayer which would result in unsightly and unsaleable "oil spottedappearance of the sole.

The ability of the hard, high melting temperature waterproofingsubstance to stay placed within the interior portion D of the leather isalso 01' importance in that this characteristic of the waterproofingsubstance enables it to increase the wear resistance of poorly fibredportions of impregnated leather out of proportion to similar poorlyfibred portions of non-impregnated leather. In this connection it willbe understood that the loose fibres are held in their matrix of watersoluble substance and hard waterproofing substances until they wear offin smaller particles rather than tear loose as is ordinarily the case.

Soles cut irom th shoulder and impregnated with waterproofing substancesin accordance with my invention have been known to wear longer thansoles cut from the better portions of nonimpregnated bend leather.

With reference to the use oi my improved leather in insoles thefollowing advantages may be noted. Since the grain layer which is nextto the foot is substantially free of waterproofing substance and is notgreas the moisture of the foot is not shut off entirely from enteringinto the leather. This is important since total exclusion of themoisture vapors from entering the insole, as occurs with ordinarywaterproofed leather in which the grain layer is substantiallyimpregrated with the waterproofing substance results in the discomfortknown as burning feet.

Chrome retanned and chrome tanned leathers are much more resistant toheat than vegetable tanned leathers. Consequently, in applying myinvention to the waterproofing of chrome retanned and chrome tannedleathers it is sometimes feasible to dispense with the previouslydescribed two-stage washing of the leather with a detergent solutionprior to the slicking or sendding operation and to employ a single stagewashing procedure in which the leather is washed with or soaked in thedetergent solution for a period of half an hour at a temperature ofapproximately 150 F. Such a procedure can be resorted to in the case ofchrome retanned and chrome tanned leathers when the waterproofingsubstance used is not extraordinarily hard and does not have too high amelting temperature. In

cases where the waterproofing compounds are extraordinarily hard andhave a correspondingly high melting temperature recourse should be hadto the two-stage detergent washing procedure described in connectionwith the waterproofing oi vegetable tanned leather.

when impregnating upper leather in accordance with my invention a veryshallow cleaning may sufilce for the light.bufilng to which upperleather is usually subjected. In this case the upper leather produced inaccordanc with my invention has the decided advantage of being much morethoroughly waterprooied than that ordinarily in use and will take a verysatisfactory polish.

Having thus described the nature of my invention and several practicalapplications thereof it will be understood that various modificationsmay be resorted to within the scope and spirit of the invention asdefined by the appended claims.

I claim:

1. In the art of waterproofing leather, the steps comprisingimpregnating the leather with a waterproofing substance selected fromthe class consisting of fats and greases which are hard and brittle atnormal temperature and have a sharp melting temperature notsubstantially below F. and then washing the leather with an aqueoussolution of sulfated fatty alcohol maintained at an efiective acidity ofapproximately pH 3.

2. In the art of waterproofing leather, the steps comprisingimpregnating the leather with a waterproofing substance selected fromthe class consisting of fats and greases which are hard and brittle atnormal temperatures and have a sharp melting temperature notsubstantially below 120 F. and then removing the waterproofing substancefrom the grain and flesh layers of the leather to a depth sufiicient topermit the leather to be bufi'ed, channelled, finished and cemented in asimilar manner to ordinary non-waterproofed leather, said removal of thewaterproofing substance from the grain and flesh layers of the leatherbeing carried out at a temperature above the melting point of thewaterproofing substance by wetting the grain and flesh layers to therequired depth with an aqueous solution of sulfated fatty alcoholdetergent which causes the leather fibre in the wetted area to swell andforce the waterproofing substance from said area by a squeezing orexpressing action and controlling the time and temperature factors ofthe wetting procedure to avoid damage to the leather by excessiveheating thereof and then promptly cooling the leather to solidify andharden the waterproofing substance remaining in the interior portions ofthe leather.

3. In the art of waterproofing leather, the steps comprisingimpregnating the leather with a hard high melting temperaturewaterproofing substance selected from the class consisting of fats andgreases which have a sharp melting temperature not substantially below120 F. and which, at temperatures substantially below said meltingtemperature, are sufliciently hard to resist being squeezed out of theleather by internal pressure created in the leather due to swelling ofthe leather fibres by absorption of water, then draining the impregnatedleather in an atmosphere well above the melting temperature of thewaterproofing substance until the surface of the leather is well drainedoff and is dry looking, then without appreciable intermediate cooling ofthe leather, washing it at a temperature of 150 F. for a relativelyshort period of time insufiicient to result in excessive heating anddamaging of the leather with an aqueous solution of a sulfated fattyalcohol effective to remove the waterproofing substance from the grainand flesh layers of the leather to a substantial depth by swelling theleather fibre and causing it to express the waterproofing substance fromthe portion of the leather wetted by said detergent, repeating thewashing operation with the solution of sulfated fatty alcohol at a lowertemperature of approximately F. and for a longer period of time to washout a further quantity of the waterproofing substance irom the grain andflesh layers, then subiecting the leather to a slicking or scuddingtreat- 75 ment at a temperature above the melting temperature of thewaterproofing substance to remove the residual waterproofing substancefrom the grain and flesh layers previously wetted by the washingsolution and then promptly cooling the leather to solidify thewaterproofing substance remaining in the interior portion of the leatherto a hard condition in which said substance has no tendency to migrateinto the previously cleaned grain and flesh layers of the leather and isresistant to being squeezed out of the interior portion of the leatherby the internal pressure created in the leather when fibres thereof areswollen by absorption of water.

4. In the art of waterproofing leather, the steps comprisingimpregnating the leather with a hard high melting temperaturewaterproofing substance selected from the class consisting of fats andgreases which have a sharp melting temperature not substantially below120 F. and

which, at temperatures below said melting tem- 20 perature. aresufilciently hard to resist being squeezed out of the leather by thepressure created in the leather when the fibres thereof are swollen byabsorption of water, then removing the waterproofing substance from thegrain and flesh layers of theleather to a depth sufilcient for bufiing,channelling, finishing and cementing purposes by washing the leather, ata temperature of approximately 150 F. and for a period of time alcohol.

' CHARLES G. SHAW.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Date Number Name 408,360 Sommers Aug. 6, 1889649,155 Bohm May 8, 1900 776,453 Case Nov. 29, 1904 1,036,267 KornacherAug. 20, 1912 1,865,783 Orthmann July 5, 1932 1,885,179 Binger Nov. 1,1932 2,089,925 Neiley Aug. 10, 1937 2,328,431

Doser et a1. Aug. 31, 1943

1. IN THE ART OF WATERPROOFING LEATHER, THE STEPS COMPRISINGIMPREGNATING THE LEATHER WITH A WATERPROOFING SUBSTANCE SELECTED FROMTHE CLASS CONSISTING OF FATS AND GREASES WHICH ARE HARD AND BRITTLE ATNORMAL TEMPERATURE AND HAVE A SHARP MELTING TEMPERATURE NOTSUBSTANTIALLY BELOW 120* F. AND THEN WASHING THE LEATHER WITH AN AQUEOUSSOLUTION OF SULFATED FATTY ALCOHOL MAINTAINED AT AN EFFECTIVE ACIDITY OFAPPROXIMATELY PH 3.